The present invention is directed to compositions Ad comprising a blend of poly(ethylene oxide) and poly(vinyl alcohol). More specifically, the present invention relates to poly(ethylene oxide) that is grafted with a vinyl monomer. The poly(vinyl alcohol) and grafted poly(ethylene oxide) blend has improved ductility.
Disposable personal care products, such as pantiliners, diapers, tampons, etc., are a great convenience. Such products provide the benefit of one time, sanitary use and are convenient because they are quick and easy to use. However, disposal of such products is a concern due to limited landfill space. Incineration of such products is not desirable because of increasing concerns about air quality and the costs and difficulty associated with separating such products from other non-incineratable articles. Consequently, there is a need for disposable products that can be quickly and conveniently disposed of without disposal in a landfill or incineration.
It has been proposed to dispose of such products in municipal and private sewage systems. Ideally, such products would be flushable and degradable in conventional sewage systems. Products suited for disposal in sewage systems and that can be flushed down conventional toilets are termed xe2x80x9cflushablexe2x80x9d. Disposal by flushing provides the additional benefit of providing a simple, convenient and sanitary means of disposal. Personal care products must have sufficient strength under the environmental conditions in which they will be used and be able to withstand the elevated temperature and humidity conditions encountered during use and storage yet still lose integrity upon contact with water in a toilet. Therefore, a water-disintegratable material having mechanical integrity when dry is desirable.
Due to their water solubility, poly(vinyl alcohol) (hereinafter PVOH) and poly(ethylene oxide) (hereinafter PEO) have potential as component materials for water-disintegratable films, fibers, and flushable products. PEO,
xe2x80x94(CH2CH2O)nxe2x80x94,
is a commercially available water-soluble polymer that can be produced from the ring opening polymerization of the ethylene oxide, 
Because of its water-soluble properties, PEO is desirable for flushable applications. However, there is a dilemma in melt processing PEO. Low molecular weight PEO resins have desirable melt viscosities and melt pressure properties for melt processing but have limited solid state properties when melt processed into structural articles, such as films, and high molecular weight PEO has limited processability.
PVOH is also a commercially available waters soluble polymer. PVOH is made by hydrolyzing poly(vinyl acetate). PVOH resins have relatively high strength compared to PEO resins. Advantageously, PVOH resins are available that are both water-soluble and thermoplastic. However, these PVOH resins have low ductility and are inherently brittle. Therefore, there is a need to improve the ductility of water soluble resins, namely PVOH, while still maintaining dry strength and water solubility.
The present invention discloses completely water-soluble blends of poly(ethylene oxide) (PEO) and grafted-PEO with poly(vinyl alcohol) (PVOH) that do not require plasticizers in order to be thermoplastically processed. Thin films can be made from the blends that have improved properties. PEO, grafted-PEO, and PVOH are all water-soluble polymers. Unmodified PVOH films not containing plasticizers are inherently brittle; i.e., they have low ductility, but they have high strength. The present invention discloses a method of improving the ductility of PVOH films, while retaining strength and water solubility.
Unmodified PEO films have inherently low strength, but have relatively greater ductility than PVOH films. Although PVOH and PEO are both hydrophilic and water-soluble, surprisingly they are not compatible with each other in melt prepared blends despite their similar polarities and water solubilities. Blends of PEO/PVOH do not display blend compatibility. Films made from unmodified PEO and PVOH are visibly hazy and contained many gel particles. The tensile properties of these films are lower in both strength and ductility than PVOH films. Haziness indicates poor compatibility as shown by increased dispersed phase size, which scatters light. The resulting film has reduced tensile properties; i.e., lowered tensile strength.
Grafted-PEO films have inherently high ductility and high tensile strength compared to unmodified PEO films, but have tensile strength significantly lower than the tensile strength of PVOH films. Films comprising a melt blend of grafted-PEO and PVOH have reduced tensile properties; e.g., reduced tensile strength, relative to PVOH films because grafted PEO has much lower tensile strength relative to PVOH but halos have increased strain-at-break. Blends of grafted-PEO/PVOH display excellent blend compatibility, greatly improved compared to unmodified PEO/PVOH blends. Thin films of the grafted-PEO/PVOH blends are much softer than PVOH films. The grafted-PEO/PVOH films have great clarity and do not contain gel particles that are observed for the unmodified PEO/PVOH films. The tensile properties of the grafted-PEO/PVOH films show greater ductility than PVOH films, and greater tensile strength than the grafted-PEO films.
In addition to the above described improvements in overall tensile properties of grafted-PEO/PVOH films, the blend morphology of the grafted-PEO/PVOH was observed and compared to unmodified PEO/PVOH films. The morphology of the grafted-PEO/PVOH films showed greatly improved compatibility between the grafted-PEO and the PVOH, compared to unmodified PEO/PVOH. Films can be made from the blends without the use of or incorporation of any plasticizers or other additives, as commonly observed in the prior art. However, plasticizers and additives can be added to the compositions of the present invention to further improve properties.
These and other features and advantages of the present invention will become apparent after a review of the following detailed description of the disclosed embodiments and the appended drawing and claims.